Polyoma viruses_MGY378_2014

Polyoma viruses_MGY378_2014 - Polyomaviruses Used to be...

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Polyomaviruses Used to be considered part of same family as papillomaviruses (called Papovaviruses) but now recognized as distinct from papillomaviruses infect several species of mammals including humans Virion: - nonenveloped icosahedral capsids about 45 nm in diameter - circular double stranded DNA genome about 5,000 bp (complexed with cellular histones)
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Examples of Polyomaviruses Polyomavirus - a mouse virus - widely studied in the lab SV40 - a monkey virus - widely studied in the lab - originally identified in monkey kidney cells used to produce polio vaccine (around 1960) - causes tumours when injected into hamsters but not in natural host
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Viral DNA is double-stranded circular Viral DNA is associated with nucleosomes composed of cellular histones H2A, H2B, H3, H4 Viral Genome
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Genome Organization The genome of all polyomaviruses is organizedinto early and late regions separated by a regulatory region. Transcription is by the cellular RNA polymerase II. Regulatory region: contains the origin of DNA replication promoters and enhancers for transcription Early region: encodes T (tumour) antigens SV40 has small t and large T antigens Polyoma has tiny, small, middle and large T antigens produced from a common transcript by alternative splicing Late region: encodes 3 capsid proteins generated from common transcript by alternative splicing
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Divergent transcription Polyoma (regulatory region) Fig 21.4 in text
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SV40
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T Antigens Tiny T: - In polyoma but not SV40 - 85 amino acids long; has not been studied Small t: - N-terminal region is same as large T - Not required for lytic cycle under most conditions - C-terminus (SV40) binds and inhibits the cellular phosphatase PP2A - Can contribute to cell transformation under some conditions (requires PP2A binding region) Middle T: - Contains small t and additional amino acids - In polyoma but not SV40 - Plasma membrane protein - Binds src kinase activating it; resulting in phosphorylation of T and some cellular proteins -
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  • Spring '14
  • DNA, Merkel Cell Polyomavirus, Polyoma, Polyomaviruses

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